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The significant increase of hydraulic fracturing activity due to technology advancements throughout Pennsylvania has resulted in an ongoing debate on how much these processes cause threats to human health and to the environment. Unconventional oil and gas development uses a method combining two technologies, horizontal drilling and hydraulic fracturing, known as unconventional shale gas extraction (Ratner & Tiemann, 2014). This process is an intensive process that has recently become an economically feasible technique for accessing low permeable (tight), high organic carbon (black) shales (Arthur et al., 2008, Barbot et al., 2013, McKenzie et al., 2012, Vidic et al., 2013). Unconventional drilling extracts the usable hydrocarbons from formations including coal- bed methane (CBM) and organic rich shale (Sovacool, 2014). The hydrocarbons within the shale have formed from the compression and pressure of organic matter within sedimentary rock over the course of millions of years, which have become trapped between two impermeable geologic formations that keep the gases confined, and present for extraction, resulting in what is referred to as an unconventional reservoir (Flaherty, 2014).

Conventional wells are drilled and completed vertically, typically targeting relatively shallow formations that exhibit greater permeability than unconventional reservoir rock. Conventional oil and gas reservoirs in western PA include the Upper Devonian Period Bradford Sandstone. Whereas the unconventional wells are a combination of vertical and horizontal drilling, targeting deeper, low-permeable formations such as the Middle Devonian Period Marcellus Shale, or the Ordovician Period Utica Shale in Pennsylvania (Baihly et al., 2010, Rahm et al., 2011, Willard,

1939). Both conventional and unconventional drilling completion methods use hydraulic fracturing. However, the intervals hydrofractured in conventional wells are shorter and use fewer fluids, about 50-100 times less water use, than during the processes relative to the development of unconventional reservoirs (Jenner & Lamadrid, 2013). The process of unconventional drilling includes the initial vertical drilling, then the cementing of large diameter steel casing across the overburden and then successively smaller diameter steel casings are cemented into place. This casing is used to isolate the fresh water bearing zone, the coal bearing intervals, shallow oil and gas bearing zones. The drilling continues to the targeted kickoff depth, at which point the drill string begins to turn and eventually becomes horizontally oriented at the unconventional reservoir, which begins

approximately 500 ft. above the top of the target formation (Rivard et al., 2014). Once the desired horizontal length, or lateral within the targeted formation is attained, the

hydraulic fracturing process begins, occurring in short segments of a few hundred feet each. This process uses the injection of large amounts of water and proppant, usually sand, at high pressures from 6,000 to 10,000 pounds per square inch (psi) (Boudet et al., 2014, Lampe & Stolz, 2015, Soeder & Kappel, 2014, Sovacool, 2014).

Historically, hydraulic fracturing fluids in western PA may have included crude oil or diesel fuel, however in present day, the composition of fracturing fluids differ from some that contain water and sand to others, such as those referred to as slickwater (Rivard et al., 2014). The slickwater fluids are comprised of primarily water and relatively low percentages compared to the total amount of fluids injected (<0.5%), which include additives such as gelling agents, corrosion inhibitors, surfactants, scale inhibitors,

2013, Sang et al., 2013, Stringfellow et al., 2014, Thurman et al., 2014). One estimate concludes that fluids contain 90.6% water, 8.95% sand or other proppant, and other chemicals making up 0.45% of the remaining fracturing fluids (Mohan et al., 2013). However, the recipe for slickwater type fluids remains a protected trade secret within many oil service companies.

These high amounts of pressure, water, and proppant cause the rock to fracture and remain open, in order to provide pathways for flow of the natural gas from the formations. The water and fluids used to pump and expand the fractures within the formation eventually flow back up and out of the well during production, consisting of formation water (naturally occurring brines), flowback fluids (return during fracturing), and produced wastewater (contains brine and flowback fluids) (Baihly, et al., 2010, Boyer, et al., 2012). Up to 90% of these injected fluids are not recovered (Abdalla et al., 2012, Cluff et al., 2014, Lester et al., 2015, Lutz et al., 2013, Orem et al., 2014, Sang et al., 2013, Stringfellow et al., 2014, Vidic et al., 2013). The produced water containing the fracturing fluids and formation brines are very high in TDS at approximately 160,000 mg/L to up to 345,000 mg/L (Chapman et al., 2012, Haluszczak et al., 2013, Kolesar Kohl et al., 2014, Phan et al., 2015). There can be over six wells drilled horizontally on one pad, extending laterally to distances greater than 2,000 meters (Cluff et al., 2014). Hydraulic fracturing methods also require 2 to 8 million gallons of water per well for a successful completion. Generally, the more water used the better the well production. This high water usage has resulted in concerns of depletion of drinking water resources and the potential for deterioration of surface and groundwater quality (Abdalla et al., 2012, Arthur et al., 2008, Boudet et al., 2014, Brittingham et al., 2014, Rahm et al.,

2011).

Depending on the composition of the flowback waters, disposal methods include use of deep injection wells, treated through industrial or municipal owned treatment facilities or can be reused for future hydraulic fracturing procedures (Lester et al., 2015, Lutz et al., 2013). In addition to the flowback and produced water, the drill cuttings, mud, and drilling fluids are considered the largest waste component of the process

(Brittingham et al., 2014, Capo et al., 2014, Engle & Rowan, 2014). The drill cuttings can have toxic and hazardous characteristics. These drill cuttings may contain arsenic,

barium, and uranium, which pose threats and challenges for disposal (Phan et al., 2015).